1. Field of the Invention
The present invention relates to an optical probe and a method of manufacturing the same, used for the super-high density recording known as "near-field optical recording" or "evanescent light recording" with an information recording device, such as an optical disk system. More specifically, the present invention relates to an optical probe using a microlens on one surface of which an evanescent-light-generating portion is formed, that is made of a light-blocking film with a micro-aperture.
2. Description of the Prior Art
One super-high density recording method for optical disk systems is known as "near-field optical recording" or "evanescent light recording", using evanescent light. Evanescent light is different from regular emitted light (travelling through free space) in that it is a surface wave that exists only near interfaces of two media with different refractive indices (and decays rapidly with growing distance from that interface). If a micro-aperture having a diameter that is not greater than the wavelength of the incident light is formed at the interface of two media with different refractive indices, evanescent light leaking into a near-field from the micro-aperture can be observed. If the near-field is not free space and another object is placed in it, then the evanescent light couples and starts to transmit energy. Applying this technology to information recording devices, it is possible to avoid diffraction, and to irradiate light with high density onto the recording medium.
A conventional technology for near-field optical recording that has been suggested uses an optical fiber probe, wherein the tip of the optical fiber is tapered extremely thin to make a tip with an aperture whose diameter is smaller than the wavelength of the incident light, and a metal film is deposited on the tapered portion (see for example U.S. Pat. No. 5,286,971). Another conventional technology, disclosed by Publication of Unexamined Japanese Patent Application (Tokkai Hei) JP-A-7-254185, is an optical head using an optical fiber probe, wherein the core portion of the fiber is made gradually thinner, and wherein the optical fiber and an air slider are formed in one piece.
Moreover, JP-A-9-198830 discloses forming a tiny tapered through hole in a slider, and directly irradiating light into the larger aperture without using an optical fiber probe, thereby generating a near-field leaking from the smaller aperture. Recently, other similar and related technologies have been reported by a number of publications.
The biggest problem with near-field optical recording is that the evanescent light leaking from the micro-aperture is extremely weak. The ratio between the energy leaking as evanescent light and the optical energy irradiated into the aperture, called "radiation efficiency", is only about 0.00001-0.0001. In other words, only an optical energy that is less than 1/1000 of the irradiation energy can be used for interaction with the optical recording medium. Consequently, there is the problem that a high-power laser has to be used, or that the optical recording speed is slow if a low-power laser is used.
To perform optical recording with a micro-aperture, a large optical energy is necessary, and it is important to have a high radiation efficiency. How high a radiation efficiency can be attained depends on the shape of the micro-aperture, the material properties, and the interaction with the optical recording medium, but many parts of the theory are still unclear, and there is a lot of research involving simulations based on Maxwell's equations. For example, light is reflected and transmitted at the metal film of the tapered portion of the optical fiber probe, and reaches the micro-aperture, but losses due to optical absorption at the metal film are still large.
The problem of optical fiber probes is that the core portion of optical fibers, which transmits the optical energy, is very small with a diameter of about 5 .mu.m, and that there is a limit for increasing the incident energy. If the incident optical energy is increased, the optical energy per area, i.e. the optical energy density increases, which can cause damage to the incident end face of the optical fiber. Another problem with optical fiber probes is that they use optical fibers that have been made very thin, and due to their pliable character, the control of their position with respect to the optical recording medium, an aspect that is indispensable when using them for optical recording, are difficult.
To form a tiny tapered through-hole directly in the slider involves a very difficult manufacturing process, and if the size of this micro-aperture varies, the entire slider has to be exchanged. Also, as in the case of optical fiber probes, there is the problem that it is not possible to introduce the optical power of a high-power laser because the hole diameter on the incident side is small. Moreover, since the light transmission is performed by reflection from the wall surfaces of the tapered through hole, the losses are large.